Water-based adhesive for the manufacture of laminated cellulosic boards comprising monolayer graphene oxide, laminated cellulosic boards obtained therewith, and methods for production thereof

ABSTRACT

A water-based adhesive for the manufacture of laminated cellulosic boards includes monolayer graphene oxide as a glue enhancer. The adhesive includes water, starch, and at least one further polymer selected from natural and soluble synthetic polymers. The adhesive further includes a glue enhancer with monolayer oxide in water and at least one further component selected from the group including stabilizing agents, gelling agents, thickening agents, anti-foaming agents, tackifyers, and damp-proofing resins, in accordance with the polymer(s).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of European PatentApplication No. 19382779.7, filed on Sep. 9, 2019, the contents of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to the field of water-based adhesives,and particularly to a glue enhancer based on monolayer graphene oxidefor such adhesives. The aqueous adhesives of the disclosure are suitablefor the production of laminated cellulosic boards, such as cardboard orpaper laminates (e.g. cardboard blanks).

BACKGROUND

Adhesives are substances that are widely used in many industries for theproduction of objects and/or materials. In many cases, adhesives areessential for correctly producing the objects and/or materials.

One of the industries that requires adhesives is the manufacture oflaminated cellulosic boards, e.g. cardboard, since cardboard plies areusually attached one to another, to provide multilayers, by means ofsuch adhesives. However, not only the plies must be attached one toanother, so as to provide a cardboard blank, but they also have to beattached in such a manner that the resulting cardboard blanks resistmanipulation by users, meteorological phenomena such as humidity, rain,cold and hot temperatures, etc. Namely, the cardboard blanks need to bereliable, and adhesives are highly relevant from this standpoint.

Graphene has been used in many different objects and materials because,in many cases, graphene makes it possible to enhance the functionalityor properties of said objects or materials. There have been a fewattempts disclosed in the prior art to incorporate graphene tocardboard, so as to improve the adhesion properties of the adhesive usedin its manufacture.

For instance, patent document EP-2886621-A1 discloses such an adhesive.Graphene nanofilaments are added to a mixture of water and starch, so asto produce the adhesive. The nanofilaments added have a diameter rangingfrom 1 to 100 nanometers and a length greater than 30 micrometers. Suchnanofilaments, however, do not mix up well with water or aqueoussolutions. Accordingly, the mixture is not really stable, and must beused within a short period of time after preparation, and the adhesiveproperties of the adhesive to which they are added are not considerablyimproved, probably due to the reduced mixing with water.

Therefore, there remains an interest in providing an adhesive that mayovercome the shortcomings of prior art solutions and that may be usedfor manufacturing laminated cellulosic boards.

SUMMARY

According to a first aspect, the present disclosure refers to awater-based adhesive for the manufacture of laminated cellulosic boards,comprising:

-   -   1) water;    -   2) starch;    -   3) optionally at least one further polymer, selected from        natural polymers or soluble synthetic polymers;    -   4) a glue enhancer, comprising monolayer graphene oxide in        water;    -   5) at least one component selected from stabilizing agents,        gelling agents, thickening agents, anti-foaming agents,        tackifyers, damp-proofing resins, in accordance with the        polymer(s).

The starch may be contained in the water-based adhesive in an amount of20 to 32 wt. %, for example in an amount between 25 and 30 wt. %.

The starch may for example be one out of maize starch, wheat starch,potato starch, pea starch, tapioca starch, or mixtures thereof.

The starch may be chemically modified, to allow the starch to functionproperly under conditions frequently encountered during processing orstorage, such as high heat, high shear, low pH, freeze/thaw and cooling.

The at least one component 5) above may for example be borax powder anda mixture of calcium hydroxide and sodium carbonate, which upondissolution in water provides caustic soda (sodium hydroxide). Sodiumhydroxide facilitates the penetration of the glue into the paper andreduces time to gel. Borax powder stabilizes the glue, by reacting withthe cooked starch, and improves glue adherence and its penetration intothe paper. It further helps to give optimal rheology. The concentrationof sodium hydroxide in the adhesive may be between 1.5 and 3.0 wt. %,and the concentration of borax in the adhesive may be between 1 and 2wt. %.

Other additional components 5) may be for example at least one ofurea-formaldehyde, which improves the moisture resistance, polyvinylalcohol or polyvinyl acetate, which improves the resistance to coldwater, or biocides, which inhibit fungal growth.

In the water-based adhesive as defined above, the natural polymer isselected from vegetable sources, protein sources or animal sources,particularly it is selected from dextrins, starches or albumins, or fromany polymers extracted from casein, blood, fish, soybean, hides orbones. The soluble synthetic polymer is selected from polyvinyl alcohol,cellulose ethers, methylcellulose, carboxymethylcellulose, andpolyvinylpyrrolidone.

The water-based adhesive may comprise only one polymer, or a mixture ofone or more polymers.

The remainder up to 100 wt. % will be water.

The monolayer graphene oxide was synthesized according to the methoddisclosed in EP15382123, which is herewith incorporated by referencewith regard to the preparation method of graphene oxide. In generalterms, the procedure is based in a modified Hummers method in which theoxidation reaction and the post exfoliation process is carried out witha high shear mixer. In this way, the graphene oxide is exfoliated at thesame time the reaction is taking place, so the yield, the oxygen contentand the monolayer content is higher than using the standard stirringmethods.

The damp-proofing resins may be, for example, ketone-formaldehyde,urea-formaldehyde or resorcinol.

In the water-based adhesives according to the present disclosure, themonolayer graphene oxide is used as an adhesive enhancer. Therefore, afurther aspect of the disclosure is the use of monolayer graphene oxideas an adhesive enhancer for water-based adhesives.

For example, the polymer may be starch. In this case, preferredcomponents 5) are caustic soda and/or borax. Preferred amounts ofcaustic soda are between 1.5 and 3 wt. % with respect to the weight ofstarch, and of borax between 1 and 2 wt. % with respect to the weight ofstarch.

A third aspect of the disclosure is a method for producing thewater-based adhesive of the disclosure as defined above, comprisingmixing starch, water and glue enhancer, said glue enhancer being asuspension of between 0.1 wt % and 0.001 wt % of monolayer grapheneoxide in water.

For example, said method comprises the steps of:

a) mixing starch into a first aqueous solution under stirring and at atemperature between 20.0° C. and 30.0° C., to obtain a first mixturecomprising between 20.0 wt % to 40.0 wt % of starch; and

b) adding to said first mixture a glue enhancer under stirring, saidglue enhancer being a second water base, comprising between 0.1 wt % and0.001 wt % of monolayer graphene oxide, thereby producing a secondmixture comprising between 0.1 wt %-10⁻⁷ wt % of monolayer grapheneoxide.

The second mixture may be directly used as a water-based adhesive.

The concentration of monolayer graphene oxide in said second mixture maybe preferably between 0.001 wt % and 10⁻⁷wt %, even more preferablybetween 10⁻⁵ wt % and 10⁻⁷ wt %, in order to reduce the costs ofmonolayer graphene oxide in the mixture.

According to further embodiments, the temperature in step a) is between24.0° C. and 26.0°, preferably between 24.5° C. and 25.5° C.

Further embodiments provide stirring of the first mixture in step a) forat least 20 minutes, and/or stirring of the second mixture in step b)the second mixture for at least 10 minutes.

The adhesive may be prepared by different methods which are known in thestate of the art.

For example, it may be prepared by a method known as “Steinhall”, whichprovides a 2 phase adhesive comprising a starch solution made with aprimary starch, called carrier, in which uncooked raw starch, i.e. asecondary starch, is suspended. The carrier is prepared by the combinedaction of heat and caustic soda on a starch slurry. This provides therequired viscosity, holding the water necessary for the gelatinizationof the secondary starch and controls the absorption into the papers aswell as the initial tack strength.

A further preparation method which may be used is the “No carrier”process. This process provides a single phase adhesive. Most of thestarch granules are partially swollen, so that the mixture is viscousenough to prevent sedimentation. The starch slurry swells progressivelywhen subjected to precise heat and alkali conditions and swellingreaction is stopped at the required viscosity using boric acid.

Minocar is a further process which may be used. The Minocar process is adevelopment of the no-carrier process, and provides a two phaseadhesive, comprising a primary portion where most of the granules arepartially swollen, in which uncooked raw starch is suspended.

A further adhesive to which the glue enhancer according to the presentdisclosure may be added is the “One-Bag Mix” (OBM) starch, which is ablend of several components which, when mixed with water, form aStein-Hall glue. The main components are:

pre-gelled (cooked and dried) starch which dissolves in the water toform the primary, carrier, component of the glue;

uncooked native starch, which is the secondary starch portion of theglue;

a mixture of calcium hydroxide and sodium carbonate, forming sodiumhydroxide (caustic soda) when dissolved in water;

borax powder.

The principal reason for using OBM is its ease of use, especially insituations where preparation facilities are limited.

A further process is the Stein Hall process, which gives a two-phaseadhesive comprising a starch solution made with the primary starch(approximately 10-20 wt % of the total amount of starch), which iscalled a carrier, into which uncooked raw starch, secondary starch(approximately 80-90 wt. % of the total amount of starch), is suspended.The carrier is prepared by the combined action of heat and caustic soda(about 1.4-3 wt. %) on a starch slurry. About 1-2 wt. % of borax aregenerally added.

The adhesive of the disclosure as defined or obtained above, may beused, for example, in the manufacture of laminated cellulosic boards.

The added monolayer graphene oxide surprisingly and unexpectedlyenhances the adhesive properties resulting from the polymer, e.g.starch, and thus it enhances the adhesive properties of the adhesiveproduced. Moreover, it seems that the presence of oxygen groups ingraphene oxide makes it possible to disperse it within the adhesive, soas to improve the adhesive properties thereof.

The resulting adhesive has a reduced drying time compared with thedrying time of an adhesive without graphene oxide. This, in turn,results in an increased productivity, as the production of objects withsuch adhesive takes less time.

Also, the mechanical properties of a product to which the adhesive isapplied, for example a single wall cardboard, a simple wall cardboard, adouble wall cardboard, etc., are also improved due to the adhesive. Somemechanical properties have been determined by FEFCO TESTING method no 9(https://find-k.ru/images/FEFCO%209.pdf), method that determines thewater resistance of the glue bond of corrugated laminated celluloseboards by immersion. Also dry peeling was tested, i.e., the resistanceto detach the cellulose layers by means of a dynamometer. Details areprovided in the Examples and Figures.

Aside from standard laminated cellulosic boards, other products may alsobe produced with an adhesive according to the present disclosure, forinstance, semi-chemical paper and plastic paper

The major component for the production of corrugated board is paper.According to the type of application and their properties, papers usedfor corrugated board production may be divided into two groups:

Papers for flat layers—liners.

Papers for corrugated layers—flutings.

Liners—depending on their manufacturing process and the componentcomposition-belong to one of the two main groups:

kraftliners,

testliners.

Kraftliners—have the best strength parameter among all the liners. Theyare composed of the cellulose pulp with a slight addition of therecycled fibre. Usually the overcoat is better glued and has a highersmoothness.

Topliner (white kraftliner) is a grade of kraftliner. Its overcoat inmost cases is made of bleached kraft pulp, while the bottom layer—of thenon-bleached stock. For the more advanced imprints white coatedkraftliners are used—the overcoat is mostly coated with a pigmentcoating colour.

Test liners—are the two-layer papers, most frequently made of 100%recovered paper. A testliner is a combination of two layers. suchconstruction enables the use of kraft pulp for the overcoat, and therecycled fibre for the bottom layer. Due to the price relation betweenthe expensive cellulose mass and the cheaper paper stock, we observe thecontiguous growth of the latter in the testliner recipes. More and morethey are entirely made of the recycled fibre. In such cases the overcoat(top layer) is dyed in order to limitate the colour of the kraft pulp.Similarly to kraftliners, testliners are manufactured with the whiteovercoat of similar whiteness. For the more advanced imprints the coatedtestliners are produced, where the overcoat is most frequently coatedwith the pigment coating colour.

In addition to the above described regular papers, special papers withspecific properties are also applied. These include among others:

-   -   wet-strength papers—converted to ensure maintaining strength        properties after wetting (PN-P-50000:1992),

fat-tight papers—high resistance to fat and grease penetration. Some ofthese papers are particularly resistant to the penetration of the abovementioned substances (PN-P-50000:1992),

barrier coated papers—with a protective layer, e.g. of polyethylene(PE), covering one or both paper sides (PN-EN 26590-1:1993),

fireproof papers—flame and/or ignition resistant (PN-P-500000:1992).

Paper for flutings (corrugated plies) in corrugated boards are dividedinto two groups:

waste based fluting (WBF)

semi chemical flutings (SC).

WBF—is manufactured exclusively of the recycled fibre. In order toimprove its mechanical properties of such fluting, starch is added toits structure. This process is popularly described as bonding. It may becarried out “in the stock” (i.e. sizing—starch is introduced into thewaste paper pulp) or starch may be additionally applied on the papersurface (surface sizing).

The semi-chemical fluting contains ca. 70% of the semi-chemical pulp,manufactured from hardwood (mostly birch) in the pulping process. Theremaining part of this pulp includes mostly the recovered paper.

The adhesive according to the present disclosure may be also applied toany of the papers mentioned above.

A further aspect of the disclosure is a method for producing a laminatedcellulosic board, comprising the steps of:

i) providing at least two cellulosic plies;

ii) applying, to at least a part of the surface of a cellulosic ply, anadhesive of the disclosure, comprising monolayer graphene oxide;

iii) contacting the surface of a further cellulosic ply to firstcellulosic ply of step ii);

iv) optionally repeating once or more times steps ii) and iii), toobtain a laminated cellulosic board.

In the method above, step iii) may further comprise applying, to atleast a part of the surface of the further cellulosic ply, an adhesiveaccording to any one of claims 1 to 4. That is, at least a part of bothsurfaces to be bond one to another have applied adhesive. Methods ofapplying adhesives to cellulosic plies are known in the art; a preferredmethod is roll coating.

The cellulosic plies may be, according to an embodiment, paper orcardboard ply.

The disclosure also refers to a laminated cellulosic board obtained bythe above method.

The disclosure further refers to a laminated cellulosic board,comprising at least two cellulosic plies attached one to another,characterized in that the at least two cellulosic plies are attached oneto another with an adhesive according to the disclosure, that is,comprising monolayer graphene oxide.

In the above laminated cellulosic boards, at least one of the cellulosicplies may be a corrugated ply, thus providing a corrugated laminatedcellulosic board.

In the above laminated cellulosic boards, at least one of the cellulosicplies may be a laminated paper.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a betterunderstanding of the disclosure, a set of drawings is provided. Saiddrawings form an integral part of the description and illustrate anembodiment of the disclosure, which should not be interpreted asrestricting the scope of the disclosure, but just as an example of howthe disclosure can be carried out. The drawings comprise the followingfigures:

FIG. 1 shows a corrugated laminated cellulose board comprising 5 layers.

FIG. 2 shows a corrugated laminated cellulose board comprising 3 layers.

FIGS. 3 and 4 show results of dry peeling tests performed with differentSamples:

FIG. 3 corresponds to a dry peeling test performed with a corrugatedboard prepared using an adhesive without the glue enhancer according tothe disclosure.

FIG. 4 corresponds to a dry peeling test performed with a corrugatedboard prepared using an adhesive comprising the glue enhancer accordingto the present disclosure.

FIG. 5 shows schematic representations of the adhesives, obtained bysome of the different methods of preparation described above.

FIGS. 6a and 6b schematically show the steps of the Stein Hall processdescribed above.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a corrugated laminated cellulose board with a plurality ofplies, particularly five, numbered 25-29, attached one to another withan adhesive, for instance an adhesive according to the presentdisclosure, i.e., comprising monolayer graphene oxide as glue enhancer.

The corrugated laminated cellulose board comprises a first planar ply25, a first corrugated ply 26, which is attached underneath the firstplanar ply 25; a second planar ply 27, which is attached underneath thefirst corrugated ply 26; a second corrugated ply 28, which is attachedunderneath the second planar ply 27; and a third planar ply 29, which isattached underneath the second corrugated ply 28. In this particularexample, the first corrugated ply 26 has a smaller fluting than thefluting of the second corrugated ply 28. This should in no case beconsidered a limitation of the disclosure, as the flutings of differentcorrugated plies may be the same or different.

One of the two major surfaces of the first and third planar plies 25 and29 (i.e., the external liners) are attached with an adhesive to a majorsurface of the first and second corrugated plies 26 and 28,respectively. Each of the second planar ply 27, first corrugated ply 26and second corrugated ply 28 have the two major surfaces thereofattached with an adhesive to a major surface of another ply. Dependingon the properties of the adhesive, the plies are glued together withmore or less adherence. The adhesive and the adherence influence themechanical properties of the corrugated laminated cellulose board 20,because a resistance of a ply may be enhanced by resistance of the otherplies, which depends, among other features, upon how strongly the pliesare glued together.

It is readily apparent that other laminated cellulose boards, bothcorrugated or not, are possible within the scope of the presentdisclosure, for instance corrugated laminated cellulose board having afirst planar ply and a first corrugated ply, or having a first planarply, a first corrugated ply and a second planar ply, or havingadditional planar and/or corrugated plies, etc. Moreover, the fluting ofthe corrugated plies may be the same or different. It is also readilyapparent that different types of paper or cardboard may be used toprepare laminated cellulose boards, such as semi-chemical paper, kraftpaper, or plastic paper, for example.

In FIG. 2 there is shown a corrugated laminated cellulosic board havingthree plies, particularly comprising a first planar ply, a corrugatedply, which is attached underneath the first planar ply; and a secondplanar ply, which is attached underneath the corrugated ply.

In FIG. 3 there is shown a corrugated laminated cellulosic board havingthree plies as described with reference to FIG. 2, the plies being gluedwith an adhesive not including a glue enhancer according to the presentdisclosure. As may be observed, the first planar ply separates from thecorrugated ply quite easily, without the ply delaminating, due to theweak adherence of the plies one to another.

In FIG. 4 there is shown a corrugated laminated cellulosic board havingthree plies as described with reference to FIG. 2, the plies being gluedwith an adhesive including glue enhancer according to the presentdisclosure. As may be observed, the first planar ply in this casedelaminates (i.e. both the planar and the corrugated layers break), dueto a stronger adherence due to the glue enhancer according to thedisclosure comprised in the adhesive used to attach the plies one toanother.

EXAMPLES

In the following, the disclosure will be further illustrated by means ofExamples and Comparative Examples. The Examples should in no case beinterpreted as limiting the scope of the disclosure, but only as anillustration of the disclosure.

Example 1 Preparation of an Adhesive According to the Disclosure

An adhesive is produced as follows: providing a volume of water of 1800L; heating the volume of water up to 25.0° C.; adding an amount ofmodified starch of 550 kg; agitating the resulting mixture for 20minutes; adding a volume of glue enhancer of 1.5 L to the mixture, thesolvent comprising water and 0.01 wt % of monolayer graphene oxide; andagitating the resulting mixture for 10 minutes. The resulting exemplaryadhesive thus has, approximately, 0.0000064 wt % of monolayer grapheneoxide.

Example 2 Dry Peeling Test

A dry peeling test was performed on several samples of corrugatedlaminated cellulose boards with and without adhesive according to thedisclosure, i.e., with and without monolayer graphene oxide therein. Inthe dry peeling test, two plies glued one to another are peeled apart.The average load required to separate the two, over the length of thespecimen is recorded, and expressed in N.

Particularly, the dry peeling test was performed on boards comprisingthree layers, as shown in FIG. 2. The 3 layers were the following:

-   -   superior ply: planar ply: T14; paper type: Test, grammage of 140        gr    -   interior ply: corrugated ply, fluting SQ15; paper type:        Semichemical, grammage of 150 gr    -   inferior ply: T14; paper type: Test, grammage of 140 gr.

Sample 1 is a corrugated laminated cellulose board according to theabove, prepared by using a glue or adhesive not comprising the glueenhancer according to the disclosure.

Sample 2 is a corrugated laminated cellulose board according to theabove, prepared by using a glue or adhesive comprising the glue enhanceraccording to the disclosure.

The results of the tests are provided in Table 1, wherein two rows ofvalues are indicated: the first row corresponding to the dry peelingbetween the superior, planar ply and the interior, corrugated ply; andthe second row corresponding to the dry peeling between the corrugatedply and the inferior planar ply.

TABLE 1 Comparison of dry peeling tests between corrugated laminatedcellulose boards with and without glue enhancer according to the presentdisclosure. Sample 1: Sample 2: Adhesive Adhesive without with glueStandard glue Standard enhancer Deviation enhancer deviation Dry peeling7.93N 0.98 delamination (superior planar ply - corrugated ply) Drypeeling 2.13N 1.05 4.74N 0.853 (corrugated ply - inferior planar ply)

In Sample 2, i.e. having glue enhancer according to the presentdisclosure, the dry peeling between the superior planar ply and thecorrugated ply results in delamination (refer to FIG. 4). Delaminationis a consequence of the high strength of the adhesive, and both planarand corrugated layers break.

In contrast, for Sample 1, i.e. without the glue enhancer according tothe present disclosure, the dry peeling between the superior planar plyand the corrugated ply the measured force was 7.93 N.

In the dry peeling test between the corrugated ply and the inferiorplanar ply, Sample 2 required a force of 4.74 N for the dry peeling,which is greater than the force for the dry peeling of the Sample 1(2.13 N).

Therefore, in both cases the resistance against dry peeling of Sample 2(comprising glue enhancer) is greater than the resistance of Sample 1(without glue enhancer) (refer to FIG. 4 versus FIG. 3, delaminationversus peeling off, without delamination).

Example 3 Determination of the Water Resistance of the Glue Bond: FEFCOTesting Method #9

Also, water resistance of the glue bond by immersion of corrugatedlaminated cellulose boards, manufactured with and without the adhesivecomprising glue enhancer according to the present disclosure, is tested,in accordance with FEFCO Testing Method #9. The water resistance of theglue of corrugated board is expressed by the amount of time that apredetermined combination of glue lines, immersed in water, resist thepulling of a suspended weight (having a mass of 250 grams) in the planevertical to the axis of the cellulosic board, at a right angle withrespect to the glue lines.

Particularly, the dry peeling test was performed on boards comprisingfive layers, according to the shown in FIG. 1. The five layers, listedfrom up to bottom, were the following:

-   -   superior, exterior planar ply: T200; paper type: Test, grammage        of 200 gr    -   first corrugated ply: small fluting, SQ150; paper type:        Semichemical, grammage of 150 gr    -   interior ply (interior liner): T140; paper type: Test, grammage        of 140 gr    -   second corrugated ply: large fluting, SQ150; paper type:        Semichemical, grammage of 150 gr    -   inferior, exterior planar ply: T200; paper type: Test, grammage        of 200 gr.

Sample 3 is a corrugated laminated cellulose board according to theabove, prepared by using a glue or adhesive not comprising the glueenhancer according to the disclosure.

Sample 4 is a corrugated laminated cellulose board according to theabove, prepared by using a glue or adhesive comprising the glue enhanceraccording to the disclosure.

It can be observed in Table 2 that Sample 4 (with the adhesivecomprising glue enhancer according to the present disclosure), featuresa longer time before it breaks, in comparison to Sample 3 (with theadhesive not including glue enhancer). In this Table 2, the waterresistance is measured between each pair of plies; also, the standarddeviation of the measured times in different tests is indicated.

TABLE 2 Comparison of water resistance of the glue bond betweencorrugated laminated cellulose boards with and without glue enhaceraccording to the present disclosure. Sample 3: Sample 4: AdhesiveAdhesive without with Glue Standard Glue Standard enhancer Deviationenhancer deviation Water resistance of the glue bond 30 s 2.3 70 s 12.2(superior planar ply-first corrugated ply with large fluting) Waterresistance of the glue bond 29 s 3.8 78 s 20.4 (first corrugated plywith large fluting - interior planar ply) Water resistance of the gluebond break break (interior planar ply - second corrugated ply with smallfluting) Water resistance of the glue bond break break (secondcorrugated ply with small fluting - inferior planar ply)

“Break” in table 1 means that the paper breaks before the adhesiveunglues.

In this text, the terms first, second, etc. have been used herein todescribe several substances or elements, it will be understood that thesubstances or elements should not be limited by these terms since theterms are only used to distinguish one substance or element fromanother.

In this text, the term “comprises” and its derivations (such as“comprising”, etc.) should not be understood in an excluding sense, thatis, these terms should not be interpreted as excluding the possibilitythat what is described and defined may include further elements, steps,etc.

On the other hand, the disclosure is obviously not limited to thespecific embodiment(s) described herein, but also encompasses anyvariations that may be considered by any person skilled in the art (forexample, as regards the choice of materials, dimensions, components,configuration, etc.), within the general scope of the disclosure asdefined in the claims.

1. A water-based adhesive for the manufacture of laminated cellulosicboards, comprising: 1) water; 2) starch; 3) optionally, at least onefurther polymer, selected from natural polymers or soluble syntheticpolymers; 4) a glue enhancer, comprising monolayer graphene oxide inwater; 5) at least one further component, selected from stabilizingagents, gelling agents, thickening agents, anti-foaming agents,tackifyers, damp-proofing resins, in accordance with the polymer(s). 2.The water-based adhesive according to claim 1, wherein the at least onefurther component 5) is borax and NaOH, or a mixture of calciumhydroxide and sodium carbonate.
 3. The water-based adhesive according toclaim 1, wherein the starch is maize starch, wheat starch, potatostarch, pea starch, tapioca starch, or mixtures thereof.
 4. Thewater-based adhesive according to claim 1, wherein the at least onefurther polymer is a natural polymer selected from the group consistingof vegetable sources, protein sources or animal sources, preferablyselected from dextrins, starches or albumins, or from any polymersextracted from casein, blood, fish, soybean, hides or bones.
 5. Thewater-based adhesive according to claim 1, wherein the at least onefurther polymer is a soluble synthetic polymer is selected from thegroup consisting of polyvinyl alcohol, cellulose ethers,methylcellulose, carboxymethylcellulose, and polyvinylpyrrolidone. 6.Use of monolayer graphene oxide as a glue enhancer for a water-basedadhesive comprising starch and at least one further polymer, wherein theat least one polymer is selected from natural polymers or solublesynthetic polymers, as defined in claim
 1. 7. A method for producing awater-based adhesive, comprising mixing starch, water and glue enhancer,said glue enhancer being a suspension of between 0.1 wt % and 0.001 wt %of monolayer graphene oxide in water.
 8. The method of claim 7,including the following steps: a) mixing starch into water understirring and at a temperature between 20.0° C. and 30.0° C., to obtain afirst mixture comprising between 20.0 wt % to 40.0 wt % of starch, andb) adding to said first mixture a glue enhancer under stirring, saidglue enhancer being a suspension of between 0.1 wt % and 0.001 wt % ofmonolayer graphene oxide in water, thereby producing a second mixture,comprising between 0.1 wt % and 10⁻⁷ wt % of monolayer graphene oxide.9. The method according to claim 8, wherein in step a) the first mixtureis stirred for at least 20 minutes, and in step b) the second mixture isstirred for at least 10 minutes.
 10. A method for producing a laminatedcellulosic board, including the following steps: i) providing at leasttwo cellulosic plies, ii) applying, to at least a part of the surface ofa cellulosic ply, an adhesive according to claim 1, iii) contacting thesurface of a further cellulosic ply to first cellulosic ply of step ii),and iv) repeating once or more times steps ii) and iii), to obtain alaminated cellulosic board.
 11. The method according to claim 10,wherein step iii) further comprises applying, to at least a part of thesurface of the further cellulosic ply, an adhesive.
 12. The methodaccording to claim 10, wherein the cellulosic ply is a paper orcardboard ply.
 13. A laminated cellulosic board, comprising at least twocellulosic plies attached one to another, wherein the at least twocellulosic plies are attached one to another with an adhesive accordingto claim
 1. 14. The laminated cellulosic board according to claim 13,wherein at least one of the cellulosic plies is a corrugated ply. 15.The laminated cellulosic board according to claim 13, wherein at leastone of the cellulosic plies is a laminated paper.